Hydrogen Sulfide (H2S) Prevents Ischemia-Reperfusion Injury (IRI) and Prolongs Survival of the Fully MHC-Disparate Lung Graft in CLAWN Miniature Swine

H2S is naturally synthesized in the mammalian body from L-cysteine. Recently, exogenous H2S has been shown to have has an anti-inflammatory or anti-oxidant effect. Since H2S is a toxic gas, translational research using large animals is essential. To attempt the H2S therapy to transplantation field, we examined the cytoprotective effects of H2S using an in situ lung IRI model (Study 1) and fully MHC-mismatched lung transplant model (Study 2) using CLAWN miniature swine. In Study 1, nine swine were divided into H2S-treated (n=4) or control group (n=5) based on the additional intravenous sodium sulfide (Na2S) treatment as H2S donor started before reperfusion. In both groups, warm ischemia was induced for 90 minutes by clamping the left pulmonary artery and veins. In Study 2, seven swine received fully MHC-mismatched lungs from donors that were rendered BD by subdural balloon inflation and subsequently ventilated for 6h before procurement with 12-days of tacrolimus postoperatively. In BD group (n=3), animals received the lung without H2S. In H2S group (n=4), both donors (3h before procurement) and recipients (before reperfusion) were treated with intravenous Na2S. Lung function was assessed with blood gases and serial lung biopsies. The expression of mRNA of proinflammatory cytokines (IL-1β and IL-6) of the lungs were quantified by real-time RT-PCR. In Study 1, H2S dramatically decreased lung IRI without adverse effects. Two hours after reperfusion, the PaO2 of the H2S-treated group was 510±17 mmHg, almost double of the control group (266±60 mmHg). Biopsies showed marked reduction of neutrophil cell infiltrates and intra-alveolar edema. In Study 2, the median survival of BD group was 21 days. H2S was effective in prolonging allograft survival (p<0.05) and the median survival was 99 days. PO2 of the graft PV in H2S group was significantly higher than in BD group (426±11 vs 349±28 mmHg; p<0.05) associated with fewer inflammatory cell infiltrates on 2-hour and 2-day biopsies. Up-regulation of proinflammatory cytokines as early as 6h after BD induction were markedly reduced by H2S. These data suggest that H2S therapy exerts cytoprotective effects on inflammatory graft damage, which led to improve not only early function but survival of the lung graft in a clinically relevant large animal model.